When Sky T&C's conflict with Ofcom

I have been looking to leave Sky, but want to take the phone number with me. I have asked an ISP some questions, but in the meantime have read that Ofcom states:

18.1 The Communications Provider shall provide Number Portability within the shortest possible time, including subsequent activation, on reasonable terms and conditions, including charges, to any of its Subscribers who so request.

However, when trawling through Sky t&c's, the following is stated:

4. Telephone numbers and transferring your number

4.1 You accept that you do not own any telephone number we make available to you. You agree not to sell or transfer any number provided to you or to advertise it in or on a BT phone box.

The number was originally provided by Sky and we are out of contract. Has anyone successfully ported a Sky generated phone number to another provider's network?